For example, U.S. Pat. No. 6,339,337 B1 discloses an infrared ray test for a semiconductor chip. The test is conducted by irradiating an infrared ray onto a bottom surface of a semiconductor chip, receiving the infrared ray reflected from a bonding pad and displaying the image of the bonding pad on a monitor. The image obtained from the infrared ray has information whether the bonding pad itself or a portion of the silicon substrate underlying the bonding pad has a defect or whether or not there is a deviation of the bonding pad with respect to the bump.
Chinese utility model CN 2791639 (Y) discloses a detecting device, which is mainly used for detecting internal defects of semiconductor material of which the band gap is larger than 1.12 eV. The detecting device for detecting internal defects of semiconductor material is composed of an optical microscope, an infrared CCD camera, video cable, a simulation image monitor, a digital image collection card, a computer and analysis process and display software.
Additionally, EP 2 699 071 A2 discloses an optoelectronic method for recording in heat diagram form the temperature distribution of land in which an infrared linescan system is used in an aircraft. The apparatus utilizes a rotary scanning mirror system receiving heat radiation through windows. The mirror system has four reflecting sides and is rotated about an axis by an electric motor. The radiation being directed by mirrors to an IR lens and thence to a row of optoelectronic receiver elements. The row of receiver elements is parallel to the axis of rotation of the mirror system, each receiver element being individually connected by a lead and an amplifying device to a corresponding one of a number of luminescent diodes.
The traditional method for finding side defects 9 in a semiconductor device 2 is shown in FIG. 1. A four sided or a five sided inspection is carried out. The semiconductor device 2 has a first side face 31, a second side face 32, a third side face 33, a fourth side face 34, a top face 4 and a bottom face 5. In the setup of FIG. 1 a camera 6 with a lens 7 looks to the bottom face 5 of the semiconductor device 2. A mirror 8 is arranged under 45 degrees with each of the first side face 31, the second side face 32, the third side face 33 and the fourth side face 34 of the semiconductor device 2, respectively. In FIG. 1 only the second mirror 82 arranged with respect to the second side face 32 and the fourth mirror 84 arranged with fourth side face 34 of the semiconductor device 2 are shown.
The setup of FIG. 1 is used obtain an image 10 (see FIG. 2) the first side face 31, the second side face 32, the third side face 33, the fourth side face 34 and the bottom face 5, respectively. The setup of FIG. 1 has significant drawbacks. The optical length 11 of the bottom face 5 view differs from the optical length 12 of the first side face 31 view, the second side face 32 view, the third side face 33 view and the fourth side face 34 view. Therefore, the focus is always a trade-off between focus on the bottom face 5 of the semiconductor device 2 and focus on the first side face 31, the second side face 32, the third side face 33 and the fourth side face 34, respectively. In case an image showing both the four side faces 31, 32, 33,34 and the bottom face 5 is to be obtained, in a process often called 5S inspection, the optical system needs a very large depth-of-focus, in order to keep both the four side faces 31, 32, 33,34 and the bottom face 5 in focus. This becomes very challenging when magnification increases.
According to a prior art method custom made mirror blocks are swapped. For a family of sizes of a semiconductor device, a custom mirror block (block with four 40-48 degree mirrors) is used. When another family of semiconductor devices needs to be inspected, the complete mirror block must be exchanged. The drawbacks are that one needs to keep expensive conversion parts and the lead time. Main disadvantages are: cost, flexibility, manual conversion, and risk of mistake. Conversion parts are needed for every family of semiconductor device sizes. These parts are custom so must be designed and manufactured when they are not yet available. This results in loss of flexibility as design must be started prior to having the family of semiconductor devices coming on-line. When the tool is converted, a line-technician or operator needs to manually change the mirror blocks. When the wrong type is mounted, damage to the tool or semiconductor device can result.
Another prior art solution is a motorization of the mirrors of the mirror block which is divided over two individual inspection stations: The front and rear images of the side faces of the semiconductor device are taken by one optical set-up that is automated. The left and right images of the side faces of the semiconductor device are taken by another optical set-up that is automated as well. So when the semiconductor device size changes, the mirrors are automatically adjusted on two inspection stations. The drawbacks are: the semiconductor devices need to pass by two inspection stations, two inspection stations increase costs and two inspection stations consume more space.
A further prior art method is that the unit or the mirror block is moved. In this concept the front/left side faces of the semiconductor device are inspected which is followed by a move of the unit or the mirror block, and then the rear/right side faces of the semiconductor device are inspected (other permutations are possible where always 2 adjacent sides are inspected). The major drawback is that the inspection is slow, which reduces throughput.
A motorization of all four mirrors 81, 82, 83 and 84 according to a prior art design is shown in FIGS. 3A to 3C. Here the set of the first mirror 81 and the third mirror 83, and the set and of the second mirror 82 and the fourth mirror 84 are moved and adapted to the size of the semiconductor device 2. The drawbacks of this arrangement are that it is very complicated and is only applicable for a limited range of sizes of the semiconductor devices.